As known, an electronic cigarette allows the vaporization of a solution (usually water-based, propylene glycol and glycerol) by heating the same by means of, precisely, electrical energy.
In detail, an electronic cigarette comprises a rechargeable battery for supplying electrical energy to a pair of terminals. These latter are fixed to a resistor, which comprises a plurality of coils wound on a wick soaked with the solution to be vaporized. The activation of the battery which supplies the terminals causes the heating of the resistor, until the vaporization of the solution takes place.
The electronic cigarette also comprises an airflow channel, which protrudes from a support element of plastic material, through which the vaporized solution, together with air, can be inhaled by a user.
From the support element two attachments also protrude, made of plastic material as well, inside which the terminals are housed (one for each attachment). In detail, the terminals protrude with a respective end beyond the attachments, in order to be welded to the coils of the resistor, whereas at the opposite ends they carry connectors, for the connection with the rechargeable battery.
The presence of these connectors causes the attachments, in order to cover the connectors at least partially, to form each an enlarged portion (i.e. a protrusion with respect to their development) at the connection zone with the support element.
The group made of plastic material just described (which is obtained by moulding) is fixed, at the respective support element, to a base, generally having a cylindrical section and being made of plastic material as well.
In particular, the fixing of the plastic base to the support element (and therefore to all the above mentioned group) can take place by means of ultrasonic welding.
The ultrasonic welding, as known, uses high-frequency sound energy to fuse plastic materials to each other at a welding zone. During the respective welding, the components to be welded (for example, the base and the group, to which the terminals are already fitted), are held together under pressure and subjected to ultrasonic vibrations.
For this purpose, a welder is used comprising: a generator, which transforms the low frequency network energy by raising the same to a higher frequency, thus producing vibrations; a converter, to transform the vibration mechanical energy at ultrasonic frequencies; a booster, which increases the amplitude of the sound waves; a sonotrode, which transmits energy in the form of vibrations to the parts that need to be fixed to each other.
In particular, the sonotrode comprises a head provided with a cylindrical cavity inside of which, during welding, the components to be welded (e.g. in the example proposed above, the airflow channel and the lateral attachments incorporating the two terminals) are partially arranged. The vibrations that the head of the sonotrode transmits onto the components to be welded causes the heating of the same, thus allowing the welding.
However, by means of the sonotrode described above it is not possible to obtain an optimal welding of the plastic components of an electronic cigarette. In fact, the irregular conformation that these components often have (for example, in the case of the base and of the group described above, due to the presence of enlarged portions of the attachments in the connection zone with the support element), only allows a partial control of the welding.
Consequently, with the aforementioned sonotrode inaccuracies in the welding often occur, and, once the components are welded together, these may present in certain areas unwanted excess of material, or non-continuous welding can occur.